1) Field of the Invention
The present invention relates to the control of temperature in an engine and, more particularly, to the use of fuel for cooling engine components and especially an exhaust nozzle such as in an aircraft engine.
2) Description of Related Art
Infrared emissions from aircraft, ships, tanks, other vehicles and structures, and the like provide an “infrared signature” that generally increases as the temperature of the components and exhausts of those devices increase. For example, the exhaust nozzle of a turbine engine of an aircraft receives the hot exhaust gases from the engine and can operate at temperatures in excess of 1000° F. Thus, the nozzle can emit significant infrared energy, thereby contributing to the overall infrared signature of the aircraft. Excessive infrared emissions, e.g., as emitted from a hot nozzle, can make the aircraft more easily detectable to infrared detection equipment, which can also use the infrared signature to identify the aircraft.
Some conventional turbine engines include an annular bypass duct, or fan duct, that surrounds the engine. A fan blows air into the bypass duct, the air flows through the duct along the length of the engine, and the air is then mixed with the exhaust gas in the nozzle. Thus, the air shrouds the high temperature combustion process within the engine and also cools the nozzle, thereby reducing the infrared signature of the aircraft. The maximum temperature of the air in the bypass duct is affected by various operating parameters including the ambient temperature of the air entering the duct, the operating temperature of the engine, the amount of air circulated through the duct, and the like. Typically, the air in the bypass duct reaches a temperature of between about 500° F. and 600° F., thereby limiting the cooling effect of the air on the engine components, especially near the nozzle, and limiting the reducing effect of the air on the aircraft's infrared signature.
Thus, there exists a need for an engine system and method for controlling the temperature of the components of the engine, such as the nozzle, and/or other components on aircraft and other vehicles and devices. Preferably, the system should be capable of cooling the components directly or by cooling a flow of air that is used for cooling.